Investigation of a critical region between corona and discharge channels in highly stressed dielectric liquids

Using several specially designed discharge chambers embodying point-point, point-plane and point-sphere electrode systems, and filled with dielectric liquid, a zone of low luminescent intensity was detected between the electrode corona and the point in the liquid at which the discharge channel originated. This dark zone is evidently the location of the mechanisms which are the critical precursors of breakdown in the liquid, and so is referred to as the critical region. It is of a general ellipsoidal shape, and for the gap lengths of 3–7mm employed has major and minor axes of about 100µm and 50µm respectively.